New factory finish on classic SIG's?

I just came home with a new SIG-Sauer P220 .45 ACP, after succumbing to a moment of weakness in the gunstore. This is, er, ahem, my fourth P220, having sold off the predecessors in prior moments of weakness (my shrink says there's a pattern in there).
Anyhoo... The finish on the slide of my new P220 seems distinctly darker and "slicker" than the 220's of my past. In fact, my prior 220's had an almost "two-tone" look in a certain angle of light, showing a thin, light blue on the slide contrasted with a deep black frame. The new gun is very well matched in color, and the slide finish just seems, well, more "slick" than any other classic SIG I've had. Could this be Nitron (thought that was only on stainless?) or Ilafon (???) or have they simply changed their blueing formulation?

By the way, this one seems to be the best SIG yet of my personal history - rock solid lockup, buttery DA trigger, absolutely sublime SA trigger. 'Tis a sexy beast, for sure:evil: .